Localization of genes influencing ethanol-induced conditioned place preference and locomotor activity in BXD recombinant inbred mice

Abstract

Genetic differences in ethanol's ability to induce conditioned place preference were studied in 20 BXD Recombinant Inbred (RI) mouse strains and in the C57BL/6J and DBA/2J progenitor strains. Male mice from each strain were exposed to a Pavlovian conditioning procedure in which a distinctive floor stimulus (CS+) was paired four times with ethanol (2 g/kg). A different floor stimulus (CS-) was paired with saline. Control mice were injected only with saline. Floor preference testing without ethanol revealed significant genetic differences in conditioned place preference, with some strains spending nearly 80% time on the ethanol-paired floor while others spent only 50% (i.e., no preference). Control mice showed genetic differences in unconditioned preference for the floor cues, but unconditioned preference was not genetically correlated with conditioned preference. There were also substantial genetic differences in ethanol-stimulated activity, but contrary to psychomotor stimulant theory, ethanol-induced activity on conditioning trials was not positively correlated with strength of conditioned place preference. However, there was a significant negative genetic correlation (r = -0.42) between test session activity and preference. Quantitative trait loci (QTL) analyses showed strong associations (P < 0.01) between conditioned place preference and marker loci on chromosomes 4, 8, 9, 18 and 19. Weaker associations (0.01 < P < 0.05) were identified on several other chromosomes. Analysis also yielded several significant QTL for unconditioned preference, ethanol-stimulated activity, and sensitization. Overall, these data support the conclusion that genotype influences ethanol-induced conditioned place preference, presumably via genetic differences in sensitivity to ethanol's rewarding effects. Moreover, several chromosomal regions containing candidate genes of potential relevance to ethanol-induced conditioned place preference have been identified.